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<title>CS 537 - Quiz #8</title>
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<b>UNIVERSITY OF WISCONSIN-MADISON
<br>
Computer Sciences Department</b>
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<b>CS 537
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Spring 1996 </b>
<td><td align=right><b>Bart Miller</b>
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<td align=center><b>Quiz #8</b>
<br>
Wednesday, April 17
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<h2>Paging to Disk</h2>
Consider computer whose operating systems is
using demand paging.
We measure the various resource utilizations under a particular workload
and see:
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<td>CPU utilization:
<td>20% of the time
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<td>Paging disk utilization:
<td>99% of the time
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<p>
Which of these (if any) should improve the CPU utilization in these
circumstances?
Why or why not?
<ol>
<li>
Get a faster CPU.
<b><p>
This system appears to be limited by the speed of the paging disk.
So, a faster CPU would only
<i>decrease</i> CPU utilization.
</b>
<pre>
</pre>
<li>
Get a bigger disk.
<b><p>
The size of the disk would allow large virtual address spaces or
allow more processes to run, but would not increase CPU utilization.
It might actually decrease it, if disk head seek time was increased.
</b>
<pre>
</pre>
<li>
Get a faster disk.
<b><p>
A faster disk would allow paging requests to be handled faster and
would probably
<i>increase</i> CPU utilization.
</b>
<pre>
</pre>
<li>
Increase the degree of multiprogramming.
<b><p>
Increasing multiprogramming
<i>might</i>
increase the utilization, if the jobs did not do much paging.
Most likely, it would just add to the disk queue, further slowing the system
(decreasing CPU utilization).
</b>
<pre>
</pre>
<li>
Decrease the degree of multiprogramming.
<b><p>
Decreasing the multiprogramming level would likely <i>increase</i>
CPU utilization if
the system was thrashing because too many jobs were competing for the
page frames.
</b>
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<hr>
<H4>
Last modified:
Wed Apr 17 14:02:29 CDT 1996
by
<a href="http://www.cs.wisc.edu/~bart">bart</a></b>
</H4>
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